Banana/Sisal Fibers Reinforced Poly(lactic acid) Hybrid Biocomposites; Influence of Chemical Modification of BSF Towards Thermal Properties

Banana/Sisal Fibers Reinforced Poly(lactic acid) HybridBiocomposites; Influence of Chemical Modification ofBSF Towards Thermal Properties

Balakrishnan Asaithambi,1 Gowri Shankar Ganesan,1 Srinivasan Ananda Kumar2

1Department of Manufacturing Engineering, Annamalai University, Chidambaram, Tamilnadu, India

2Department of Chemistry, Anna University, Chennai, Tamilnadu, India

The present work focused on thermal behavior of bio-composites based on poly(lactic acid) (PLA) reinforcedwith untreated and benzoyl peroxide (BP) treatedbanana/sisal fibers (BSF) combination. Fabrication ofbiocomposites was performed by extrusion followedby injection molding. Fourier transformed infrared(FTIR) spectral technique ascertained the nature ofbonding between BSF and PLA. The thermal propertiesof virgin PLA, UT-BSF/PLA, and BP-T-BSF/PLA compo-sites were studied by DSC and TGA analysis. DSCanalysis indicated no significant changes in the glasstransition temperature (Tg) and melting temperature(Tm) of virgin PLA, UT-BSF/PLA, and BP-T-BSF/PLAcomposites and no sign of crystallization for both vir-gin PLA, UT-BSF/PLA composites. However, crystalli-zation was observed in BP-T-BSF/PLA composites.The BP-T-BSF/PLA composite exhibited a delayed ther-mal degradation pattern from TGA analysis when com-pared to that of UT-BSF/PLA composites and virginPLA as well. Further, the effect of BSF treatment andhybridization of BSF with PLA on the degree of crystal-linity (Xc) were explored in detail. The above said com-posites were also investigated through scanningelectron microscope (SEM) micrographs to examinethe adhesion between the PLA and BSF. In addition,the results of SEM acquired are in good agreementwith the data resulted from FTIR and thermal charac-terization. POLYM. COMPOS., 00:000–000, 2015. VC 2015 Soci-ety of Plastics Engineers

INTRODUCTION

In recent years, industries are taking up much more

efforts to reduce the use of petroleum-based fuels and

commodities due to the augmented environmental aware-

ness. The systematic research is now headed towards

biocomposite materials for cleaner and protected environ-

ment. Amidst the dissimilar types of biocomposites, those

which comprise natural fibers (NF) and natural polymers

play a key role in the development of new materials [1].

NF have become an inevitable alternative to conventional

synthetic fillers like glass or carbon fibers due to their

low price and density, least tool wear for the duration of

processing, environmental affable, and biodegradable

character. Hence, biopolymers reinforced with NF resulted

in a large number of applications to bring them at equiva-

lence with improved quality than synthetic composites [2,

3]. Poly(lactic acid) (PLA)-based materials have been

incorporated with mineral and bio-based fibers in order to

overcome their limitations to produce PLA composites

with enhanced properties. PLA is a brittle polymer and

has relatively much lower thermal and impact resistance

than that of conventional thermoplastics. Exclusively, bio-

fillers derived from renewable resources are consequently

considered an ideal biomaterial for load bearing applica-

tions, such as orthopedic fixation equipments as sutures,

pins, scaffolds, and drug delivery devices. Such strategies

are of a great deal of interest for a possible use of rein-

forced PLA materials as alternatives to the currently exist-

ing traditional synthetic fibers in composite materials

owing to their sustainable supply and environmentally

benign production [2–4]. Therefore, using cellulose micro

fibrils like abaca, curaua, henequen, pineapple, sisal,

banana, flax, hemp, jute, ramie, coir, kapok, and oil palm

as reinforcement in polymers is extraordinary. In the

midst of the NF mentioned above, flax, bamboo, sisal,

hemp, banana, jute, and wood fibers are still fascinating

as their final utilization proved to be excellent reinforce-

ment materials in polymeric matrix composites. In this

context, banana fibers (BF) are noteworthy for their out-

standing properties that are derived by alkaline pulping

and steam explosion, to produce cellulose fibers and use

of such BF in various polymers confirmed promising

results in the past, particularly in the presence of interfa-

cial bond agent [1, 5]. On the other hand, sisal fibers (SF)

Correspondence to: Balakrishnan Asaithambi; e-mail: asaithambi100@

yahoo.com

DOI 10.1002/pc.23668

Published online in Wiley Online Library (wileyonlinelibrary.com).

VC 2015 Society of Plastics Engineers

POLYMER COMPOSITES—2015

are considered as extremely versatile material because of

their high strength and bonding with polymer matrices

and their applications as twines, cords, upholstery, pad-

ding, and mat making for automobiles, fishing nets, and

ropes for the marine and agriculture industry as well [2,

6]. The major serious issue with NF is their deliquescent

nature, which leads to lack of bonding between the fibers

and the hydrophobic polymer matrices. This hydrophilic

character of NF seriously lowers the thermal properties of

the fibers themselves. Furthermore, wetting of the NF

with the matrix is another problem that leads to difficulty

in mixing and makes the resultant biocomposites with a

very weak interface leading to irregular stress transmit

between the adjacent regions of the biocomposites. There-

fore, treatment of NF by various chemical treatments like

mercerization, acrlylation, acetylation, silane, permanga-

nate, and benzoyl peroxide (BP) was done to modify the

fiber surfaces that offer enhanced adhesion strength to the

fiber-matrix interface. Hence, a chemical treatment of

banana/sisal fibers (BSF) by mercerization (using NaOH)

is mandatory to enhance their surface roughness, and to

promote active surface area available for intimate contact

with the matrices by partially removing the lignin, hemi-

celluloses, and other residues from the surface of BSF.

Moreover, BP treatments of BSF have resulted in increase

of thermal stability to a temperature around 240 8C [1, 2,

6, 7]. The higher cost, lower toughness, and thermal sta-

bility imparted by PLA restrict its usage for different end

user applications. Hence, the addition of BSF has been

suggested as a means of improving thermal properties of

PLA in order to maintain their valid rank in the field of

successful polymers. Therefore, hybrid composite that

contains BF and SF proves to be beneficial as one type of

fiber could balance with what is required in the other one.

As a result, stability in price and concert could be attained

through proper material design. As a result, PLA has been

chosen as matrix material and BSF as reinforcing material

for our recent study to fabricate hybrid biocomposites,

which can offer improved properties that are required for

various engineering applications [6–11]. Moreover, the

hybridization of BSF with PLA can be done by extrusion

process in a twin-screw extruder and the extruded compo-

sites were further injection molded to test specimens

[8–12]. Furthermore, the intention of this research is to

study the thermal properties of virgin PLA, UT-BSF/PLA,

and BP-T-BSF/PLA biocomposites by means of Fourier

transformed infrared (FTIR) spectra, DSC, and TGA char-

acterization techniques. The interfacial adhesion between

the fiber and the matrix was explored through scanning

electron microscope (SEM).

EXPERIMENTAL

Materials

BF and SF were purchased from Kolvel Fibers,

Nagerkovil and Vibrant Nature, Chennai, Tamilnadu,

respectively. PLA (IngeoTM Biopolymer 3052 D)

designed for injection molding with a density of 1.24 g/

cm3, molecular weight (Mw): 180,000, Tm in the range of

150–165 8C, and Tg of about 55–65 8C in pellet form from

Nature Works LLC, Minnetonka product was provided by

Harita NTI Ltd, Chennai, Tamilnadu. Sodium hydroxide

(NaOH) and BP pellets which were used in chemical

modification of the BSF were supplied by Merck,

Germany.

Chemical Modification of BF and SF

The BFs were subjected to NaOH treatment prior to

BP treatment in order to remove the lignin, hemicellulo-

ses, pectin, wax, and other residue materials from the

fibers, so as to provide adequate roughening to the fiber

surface. The BF were soaked in 5 wt% NaOH solution at

room temperature for 2 h. Furthermore, the BF were

washed numerous times with distilled water to remove

NaOH solution sticking on the BF surface. Finally, acetic

acid was used to adjust the pH value of the fibers. BF,

subsequent to acetic acid treatment were taken out and

dried for 2 days at room temperature and then dried at

80 8C for 24 h in a vacuum oven. This dried BF were

immersed in 6 wt% BP with acetone solution at 70 8C for

30 min and washed several times with distilled water to

remove excess BP sticking on the fiber surface. Lastly,

acetic acid was added to the BP treated BF to adjust the

pH once again. The fibers were dried at room temperature

for 2 days, followed by a vacuum oven drying at 80 8C

for 24 h. PLA was dried for overnight in an oven at 50 8C

and stored in an air tight bag as per the reported proce-

dure [1, 2, 5–7, 12]. The surface modification of SF using

NaOH followed by BP was carried out in a similar proce-

dure followed for BF. Later, fibers were chopped into

desired size as discontinuous fibers for the fabrication of

BSF-PLA biocomposites.

Fabrication of BSF Reinforced PLA HybridBiocomposites

Extrusion followed by injection molding was per-

formed to fabricate BSF reinforced PLA composites. The

virgin PLA particles and UT-BSF (chopped) with the

ratio of 70:30 wt% were blended in a twin-screw extruder

machine (screw diameter of 28 mm, L/D ratio of 40). In

the extruder, the temperatures of the feeding zone, the

barrel, and the die was set to 160 8C, 180 8C, and 175 8C,

respectively. The screw speed of 100 rpm was retained

during extrusion process, which was carried out for

15 min at a rate of 10 mm/s; hereafter, the strands

acquired from extrusion were pelletized.

Extruded pellets were dried at 50 8C in a vacuum oven

for 24 h and sealed in polyethylene bags. Similarly, the

blending of BP-T-BSF/PLA composites was carried out

in a similar procedure followed for UT-BSF/PLA compo-

sites. Consequently, the UT-BSF/PLA extruded pellets

2 POLYMER COMPOSITES—2015 DOI 10.1002/pc

were processed by means of injection molding, which

was executed at a temperature of 180 8C, injection back

pressure of 7 bars and time of 0.95 s, injection machine

speed of 60 mm/s, and mould temperature of 30 8C,

respectively (screw diameter of 30 mm with L/D ratio of

20 at 60 ton capacity) to obtain hybrid biocomposite test

specimens. The virgin PLA and BP-T-BSF/PLA biocom-

posite test specimens were fabricated by IM with the

same procedure adopted for UT-BSF/PLA composites.

The test specimens were subjected to annealing at a tem-

perature of 80 8C in an oven as long as 24 h [3, 9–12].

CHARACTERIZATION AND PROPERTIES

FTIR Spectra

FTIR spectroscopy was used to confirm whether chem-

ical treatment had improved the properties of virgin PLA,

UT-BSF/PLA, BP-T-BSF/PLA biocomposites. FTIR spec-

tra of the samples were recorded in the wavelength range

from 4,000–400 cm21 with 50 scans using a resolution of

4 cm21 by Bruker IFS 66 spectrometer in attenuated total

reflectance mode.

DSC

Samples of around 5 mg of virgin PLA, UT-BSF/PLA,

BP-T-BSF/PLA biocomposites were scanned from 25 to

400 8C at the heating rate of 10 8C/min by employing

DSC (TA instruments 2000 Q10 V9.0 Build 275) pro-

vided by means of a cooling attachment and interfaced to

a computer, concealed by a nitrogen atmosphere by purg-

ing gas 50 ml/min to detect the melting characteristics of

the virgin PLA and its composites.

TGA

The thermal stability of virgin PLA, UT-BSF/PLA,

and BP-T-BSF/PLA biocomposites was evaluated by ther-

mogravimetric analyzer (TGA-Perkin Elmer-7). Samples

of about 10 mg were heated from 25 to 800 8C at a heat-

ing rate of 20 8C/min under nitrogen atmosphere by purg-

ing 50 ml/min gas.

SEM Analysis

The microstructure of the biocomposites and the BSF/

PLA interface were studied by SEM (JEOL JSM 6060).

The micrographs from SEM were used to investigate UT-

BF (untreated BF), T-BF (treated BF), UT-SF (untreated

SF), T-SF (treated SF), the distribution of BSF within

PLA, and their nature of adhesion with each other. The

samples were coated with a thin layer of gold before

scanning observation was made in order to increase the

sample conductivity and also to avoid electrostatic charg-

ing during sample examination.

RESULTS AND DISCUSSION

FTIR Spectrometry

Figure 1 shows the FTIR spectra for virgin PLA, UT-

BSF/PLA, and BP-T-BSF/PLA hybrid biocomposites, in

the region of 4,000–400 cm21. In this FTIR analysis, the

region of concern was between 1,800 and 1,300 cm21

where active ester and methyl groups of PLA are

detected. The lignin (aromatic C@C) peak at 1,560 cm21

from FTIR spectra was noticeable for UT-BSF/PLA com-

posites. The band between 1,700 cm21 and 1,650 cm21

corresponds to the stretching of the carboxyl, acetyl car-

bonyl groups that belong to hemicelluloses of UT-BSF

and broadening of the OAH peak toward higher fre-

quency region reveals the existence of water molecules

due to the major moisture content in UT-BSF/PLA com-

posites. However, BP-T-BSF/PLA composite showed a

sharp decrease in the peak intensity of OAH at

3,500 cm21 indicating an enormous reduction in the water

content. This lowering of peak intensity found in BP-T-

BSF/PLA in the region around 1,770 cm21 is clearly evi-

dent due to the incomplete dissolution of hemicelluloses,

which is mainly due to the elimination of acetyl group

present in hemicelluloses after alkali treatment [5,

13–16]. FTIR of PLA, when compared against BP-T-

BSF/PLA composite shows more intensity for the C@O

stretch and ACAOA groups of ester bonds, at

1,730 cm21 where active ester and methyl groups of PLA

are located. This corresponds to the effective adhesion of

the BSF with the PLA, which had happened as a conse-

quence of the BP treatment [14–18]. The peak at

2,900 cm21 in UT-BSF/PLA may be associated to CAH

stretching in methyl and methylene groups. This peak

may hardly be detectable after alkaline treatment of BSF

in BP-T-BSF/PLA composites [5, 13, 14, 19, 20].

FIG. 1. FTIR spectra of virgin PLA, UT-BSF/PLA, and BP-T-BSF/

PLA hybrid biocomposites. [Color figure can be viewed in the online

issue, which is available at wileyonlinelibrary.com.]

DOI 10.1002/pc POLYMER COMPOSITES—2015 3

Likewise, the intensity of the OAH peak at 3,500 cm21

had also reduced, indicating a decrease in the water con-

tent of the BP-T-BSF/PLA composite, which was

expected due to changes in BSF surface accomplished by

chemical treatment using NaOH followed by BP [13, 14,

16, 21].

Effect of BP Treated Fiber Surface on ThermalProperties of BSF/PLA Composites–DSC

The thermal properties like glass transition temperature

Tg (8C), crystallization temperature Tc (8C), enthalpy of

crystallization temperature DHc (J/g), melting temperature

Tm (8C), heat of melting DHm (J/g) and degree of crystal-

linity Xc (%) of virgin PLA, UT-BSF/PLA, and BP-T-

BSF/PLA hybrid biocomposites obtained from the DSC

scans are summarized in Table 1. The degree of crystal-

linity was calculated based on the following Eq. 1

Xcð%Þ5DHm

f � DHom

3100 (1)

where DHm is the heat of melting (J/g) of test specimen

and DHom is the heat of melting for 100% crystalline PLA

taken as 93.1 J/g and f as weight fraction of PLA from

the literature [11, 12].The DSC scans of virgin PLA

(extruded & injection molded), UT-BSF/PLA and BP-T-

BSF/PLA hybrid biocomposites are illustrated respec-

tively in Fig. 2. From Fig. 2, it can be inferred that three

peaks observed in the case of virgin PLA are attributed to

Tg (64 8C), Tm (153 8C), and Td (251 8C), respectively. In

contrast to this observation, UT-BSF/PLA composite (see

Fig. 2) showed three peaks corresponding to Tg, Tm, and

Td at temperatures 61 8C, 151.41 8C, 217 8C followed by

an oxidation peak at To (304 8C), where as BP-T-BSF/

PLA composite (Fig. 2) exhibited three peaks correspond-

ing to Tg, Tm, and Td at 63 8C, 153 8C, 301 8C in addition

to a crystallization peak Tc observed at (109 8C).

Effect of UT-BSF and T-BSF Toward Tg & Tm of PLA

It was observed that the Tg values of UT-BSF/PLA

and BP-T-BSF/PLA hybrid biocomposites dropped to

61 8C and 63 8C, respectively, compared to the Tg (64 8C )

of virgin PLA. The inclusion of UT-BSF into PLA

decreases Tg to 61 8C indicating an occurrence of change

in degree of plasticization. This may be attributed to the

formation of free volume as a consequence of slack stuff-

ing of filler within the PLA enabling free mobility of the

PLA matrix chains signifying the poor interaction

between PLA and UT-BSF [3, 10, 18, 19, 22]. This inter-

action had however been enhanced by BP treatments of

BSF, which in turn caused an increased value of Tg (63C)

for BP-T-BSF/PLA biocomposites. This substantiates BP-

T-BSF/PLA biocomposites further reduces the macromo-

lecular mobility through strong adhesion between PLA

and BSF as pointed out in FTIR spectral data illustrated

in Fig. 1. From these results, it is evident that biocompo-

sites having UT-BSF surface had inferior influence on the

nucleation ability in comparison with BP-T-BSF/PLA

composites [15, 17, 21]. This was well supported by SEM

micrographs. For all above composites, the melting endo-

thermic peaks indicate that the inclusion of BSF in virgin

PLA did not change the melting temperature significantly.

The Tm of the UT-BSF/PLA biocomposite slightly shifted

to a lower temperature, indicating its ineffective heat

transfer. This may be caused by the inferior bonding

between PLA matrix and UT-BSF [5, 11, 18].

Effect of UT-BSF and T-BSF Toward Tc & Xc of PLA

No crystallization peak for PLA was noticed seems

quite interesting. The absence of crystallization peak may

be due to the air quenching of virgin PLA during IM pro-

cess and presence of moisture, which would have resulted

FIG. 2. DSC scans for virgin PLA (extruded & injection molded), UT-

BSF/PLA, and BP-T-BSF/PLA hybrid biocomposite. [Color figure can

be viewed in the online issue, which is available at wileyonlinelibrary.

com.]

TABLE 1. Results from the DSC scan for virgin PLA, UT-BSF/PLA, and BP-T-BSF/PLA hybrid biocomposites.

Materials Tg (8C) Tc (8C) DHc (J/g) exo Tm (8C) DHm (J/g ) endo Xc (%)

Virgin PLA (extruded &

injection molded)

64 – – 153 30 32

UT-BSF/PLA composite 61 – – 151 17 26

BP-T-BSF/PLA composite 63 109 18 153 26 40


into a highly amorphous polymer state. This implies that

the pellets of virgin PLA were of low crystalline in nature

[3, 10, 17, 21, 22]. It was clearly evident from the Fig. 2

that there was no crystallization peak in UT-BSF/PLA

composites representing the fact that the presence of any

untreated fiber in PLA can depreciate crystallization [10].

Table 1 also reveals that the Xc of UT-BSF/PLA biocom-

posite was considerably reduced to 26% in comparison

with virgin PLA whose Xc value was 32%. This may be

attributed to the poor interface between PLA and UT-BSF

[8]. Moreover, the values of DHm decreased with the

addition of the fiber. This decrease in DHm indicates

more reduction in energy required to melt the UT-BSF/

PLA biocomposite as compared with PLA and the fiber

may disrupt the crystallite formation of PLA, leading to

lower levels of crystallinity of the UT-BSF/PLA compo-

sites [8, 15, 19]. It was also interesting to note a crystalli-

zation exothermic peak Tc (109 8C) observed in T-BSF/

PLA biocomposite. This may be owing to the reorganiza-

tion of amorphous domains into crystalline regions on

account of the decreased macromolecular flexibility and

mobility. This specifies that T-BSF act as nucleating

agent and promotes better crystallization by enabling

PLA chains be entangled and covalently bonded to their

surface and thus becomes less mobile. Studies have

revealed the effect of T-BSF as nucleating agent enabling

their surface roughness and process of extrusion followed

by IM process assist the crystallization [17, 21, 23].

Hence, BP-T-BSF/PLA biocomposites exhibited the maxi-

mum in degree of crystallinity to 40% unlike UT-BSF/

PLA biocomposites, whose degree of crystallinity was

26%. This may be due to the removal of hemicelluloses

by alkalization subsequently BP [5, 7, 11, 13, 17, 21].

Further, the standard error bars are shown for the average

values related to degree of crystallinity (Fig. 3) for virgin

PLA (Extruded & injection molded), UT-BSF/PLA and

BP-T-BSF/PLA hybrid biocomposites.

Effect of UT-BSF and T-BSF Toward Td & To of PLA

DSC scans of Fig. 2 describe the decomposition and

oxidation of virgin PLA, UT-BSF/PLA, and BP-T-BSF/

PLA hybrid composites. The thermal decomposition tem-

perature of virgin PLA observed beyond 250 8C may be

caused due to occurrence homolysis of polymer back-

bone. McNeill and Leiper have demonstrated that the

thermal decomposition of virgin PLA above 250 8C was

caused by degradation of acetaldehyde, involving a com-

plex chain reaction leading to the formation of methane

and carbon monoxide. In contrast to this observation,

intramolecular and intermolecular ester exchange, cis-

elimination, radical and concerted non-radical reactions

resulting in the formation of CO, CO2, acetaldehyde, and

FIG. 3. Degree of crystallinity for virgin PLA, UT-BSF/PLA, and BP-

T-BSF/PLA hybrid biocomposite with standard error bars. [Color figure

can be viewed in the online issue, which is available at wileyonlineli-

brary.com.]

FIG. 4. TGA thermograms of virgin PLA, UT-BSF/PLA, and BP-T-

BSF/PLA hybrid biocomposite. [Color figure can be viewed in the

online issue, which is available at wileyonlinelibrary.com.]

TABLE 2. Results from the TGA thermograms for virgin PLA, UT-BSF/PLA, and BP-T-BSF/PLA hybrid biocomposites.

Materials Td min (8C) Td max (8C)

Weight

loss (%)

Residue

weight (%)

Max.

DTG (8C)

Virgin PLA (extruded &

injection molded)

334 366 98 0.23 355

UT-BSF/PLA composite 342 373 95 2.32 361

BP-T-BSF/PLA composite 349 378 98 0.72 369


methyl ketene was reported by L.T. Lim et al. [3]. It

was reported by Sinha and Rout et al. [13], that in cellu-

lose fibers, lignin may degrade at a temperature 217 8C

in UT-BSF/PLA hybrid composites while the other poly-

saccharides such as cellulose degrade at higher tempera-

ture. Therefore, the peak which appears at temperature

higher than 200 8C indicates the decomposition of cellu-

lose in the fibers. The first exothermic hump in the DSC

scan for UT-BSF/PLA about 304 8C is due to the thermal

degradation of hemicellulose and the glycosidic linkages

of cellulose. Paunikallio et al. [13] observed a similar

trend for untreated jute fiber reinforced composite [16,

23]. In BP-T-BSF/PLA hybrid composites, the region

between 150 and 300 8C shows no exothermic or endo-

thermic reactions, which suggest that the T-BSF are sta-

ble between these temperatures. This may be due to the

removal of hemicellulose from the fiber after alkali

treatment [6, 13, 23]. The endothermic peak at about

350 8C indicates the degradation of cellulose, leading to

the formation of char in BP-T-BSF/PLA hybrid

composites.

Effect of BP Treated Fiber Surface on ThermalProperties of BSF/PLA Composites–TGA

TGA measures the change in the weight of a sample

as a function of temperature in a controlled atmosphere

leading to decomposition, oxidation (formation of new by

products), or loss of volatiles. The thermograms of virgin

PLA, UT-BSF/PLA, and BP-T-BSF/PLA composites are

illustrated in Fig. 4, respectively. The obtained results are

given in the Table 2. TGA thermograms exhibited a sin-

gle stage degradation pattern for all the materials. The

virgin PLA had an earlier initial degradation Td min

(334 8C) than UT-BSF/PLA Td min (342 8C) and BP-T-

BSF/PLA Td min (349 8C) composites. However, the huge

weight loss (98 %) and low residue weight (0.23%)

occurred in virgin PLA indicates its substandard thermal

stability in comparison with the other two PLA/BSF com-

posites. The weight loss of 98% observed in virgin PLA

may be attributed to the degradation of PLA by end chain

scission leading to the formation of lactide monomers and

cleavage of ester bonds that occurred at higher tempera-

tures [3, 17]. In the case of UT-BSF/PLA composite, the

first step transition onset peak (Fig. 4.) of Td min starts

from 342 8C and ends with Td max at 373 8C with a corre-

sponding weight loss of 95% from 10.16 to 0.25 mg. The

reason for the delayed thermal degradation exhibited by

UT-BSF may be due to inclusion of BSF into PLA lead-

ing to a better thermo-oxidative stability of the resultant

composites was also reported by Y.B.Tee and S.N. Mon-

teiro et al. [16, 27]. And this may possibly due to the

presence of lignin that normally degrades at higher tem-

perature because of its inherent heat resistance towards

decomposition and also owing to the barrier effect offered

by UT-BSF within the PLA. Finally, the decomposition

occurred at 373 8C may be associated to non-cellulosic

materials (D-xylose and L-arabinose) in the fibers, involv-

ing aromatization from lignin and dehydration reactions,

which was mainly related to the breaking of the chemical

bonds of the proto-lignin present in the UT-BSF. E.S.

Zainudin et al. [24] also reported that the mechanism of

degradation in BSF includes the decomposition of hemi-

celluloses and cellulose degraded by heat much before

the degradation of lignin. A similar trend was observed in

FIG. 5. Maximum derivative thermograms for virgin PLA, UT-BSF/

PLA, and BP-T-BSF/PLA hybrid biocomposite with standard error bars.

[Color figure can be viewed in the online issue, which is available at

wileyonlinelibrary.com.]

FIG. 6. Fractured micrograph of extruded and injection molded virgin PLA from SEM at (a) 3 200 & (b) 3 500 magnifications.


our study indicating above decomposition mechanisms.

Hence, the UT-BSF/PLA composites showed better ther-

mal degradation pattern in comparison with virgin PLA

[9, 11, 13, 14, 17, 25, 26]. In case of BP-T-BSF/PLA

composite, the first initial step transition onset peak (Fig.

4) of Td min starts at 349 8C and ends with Td max at

378 8C corresponds to a weight loss of 98 % from 3.94 to

0.03 mg. It is well known that BP treatment next to alka-

lization would have an effect on the cellulose structure

leading to better thermal delayed initial degradation and

FIG. 7. Fractured micrograph of UT-BF surfaces at (a) 3 120 and (b) 3 500 magnifications, BP modified BF surfaces at (c) 3 120 and (d) 3 500 mag-

nifications. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

FIG. 8. Fractured micrograph of UT-SF surfaces at (a) 3 120 and (b) 3 500 magnifications), BP modified banana sisal surfaces at (c) 3 120 and

(d) 3 500 magnifications. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]


final decomposition temperature than UT-BSF/PLA and

virgin PLA. This may be attributed to partly dissolved

hemicellulose and lignin of BSF during mercerization fol-

lowed by peroxides, which further react with the hydro-

gen group of the matrix and cellulosic fibers achieving

various levels of success in improving its strength and fit-

ness followed by BSF-PLA adhesion [1, 9, 11, 13, 19,

27]. The final degradation of BP-T-BSF/PLA biocompo-

sites occurred at 378 8C may be associated to the thermol-

ysis reaction of cellulose by the cleavage of glycoside

bond, CAH, CAO, CAC bonds, as well as by dehydration,

decarboxylation, and decarbonylation [7, 13, 20]. Further-

more, the final delayed decomposition of BP-T-BSF/PLA

biocomposites may be due to hybridization of BF and SF

which restricted the molecular movement by cross-linking

reaction between matrix and BSF, thus could augment the

improved thermal stability [16, 20, 23, 26]. Further, the

initial decomposition temperature of UT-BSF/ PLA com-

posite at 342 8C, was enhanced to 349 8C of BP-T-BSF/

PLA composite after mercerization followed by BP treat-

ment. These results showed that delayed thermal degrada-

tion of T-BSF/PLA composites (378 8C) have superior

thermal properties compared to that of UT-BSF/PLA

composites (373 8C) and virgin PLA (366 8C) and DTG

thermograms of above materials confirm too about ther-

mal stability [7, 9, 11, 13, 17, 19, 20, 24–26]. Further, the

standard error bars are shown for the average values

related to maximum derivative thermograms (Fig. 5) for

virgin PLA (Extruded & injection molded), UT-BSF/

PLA, and BP-T-BSF/PLA hybrid biocomposites. The

TGA results acquired from thermal data can also be vali-

dated from FTIR spectra and SEM micrographs. The

SEM Fractured micrograph of extruded and injection

molded virgin PLA illustrated in Fig. 6 at (a) 200 & (b)

500 magnifications shows a smooth and wavy look sur-

face, which clearly reveals the inherent brittle nature of

PLA (extruded and injection molded). The SEM micrographs

depicted in the Fig. 7 show UTBF surfaces at (a) 120 and (b)

500 3 magnifications, BP modified BF surfaces at (c) 120

and (d) 500 3 magnifications. Fig. 8 depicts fractured micro-

graphs of UT-SF surface at (a) 120 and (b) 500 3

magnifications), BP modified banana sisal surface at (c) 120

and (d) 500 3 magnifications, Fig. 9 SEM micrograph of

fractured surface of UT-BSF/PLA hybrid composite, and Fig.

10 SEM micrograph of fractured surface of BP-T-BSF/PLA

hybrid composite at (a) 120 and (b) 500 3 magnifications.

The presence of hemicellulose, lignin, waxy substances were

clearly seen in both UT-BF and UT-SF illustrated in Fig. 7a

and b and Fig. 8a and b, indicates the enhanced hydrophilic

nature of BSF. In case of T-BF and T-SF, alkalization fol-

lowed by BP promotes rough surface on BSF which can be

seen in Fig. 7c and d and Fig. 8c and d. Hence, removal of

exterior materials alter the fibrils more competent of rear-

ranging themselves in a dense manner leading to a closer

packing of the cellulose chain within the BP-T-BSF/PLA

composites. However, the SEM micrograph of the UT-BSF/

PLA composite depicted in Fig. 9 exhibits the presence of

voids and cavities in the composite. The voids could have

either occurred because of fiber debonding or poor wetting

during production of composite. The existence of such voids

in UT-BSF points out its poor matrix/fiber adhesion. In con-

trast, the SEM images of BP-T-BSF/PLA composites, illus-

trated in Fig. 10 did not show any such voids that were

predominantly seen in Fig. 9. This clearly indicates the supe-

rior compatibility and effective dispersion of BSF throughout

PLA matrix as a consequence of IM process. This could be

FIG. 9. SEM micrograph of fractured surface of UT-BSF/PLA hybrid

composite. [Color figure can be viewed in the online issue, which is

available at wileyonlinelibrary.com.]

FIG. 10. SEM micrograph of fractured surface of BP-T-BSF/PLA hybrid composite at (a) 3 120 and (b) 3 500 magnifications. [Color figure can be

viewed in the online issue, which is available at wileyonlinelibrary.com.]


one of the possible reasons why an improved thermal stability

was imparted by BP-T-BSF/PLA composites than virgin

PLA and UT-BSF/PLA composites [5, 7, 10–12, 15, 19].

CONCLUSIONS

Manufacturing of biocomposites based on PLA rein-

forced T-BSF and UT-BSF combination was performed

by extrusion followed by injection molding. Thermal

characterization of virgin PLA, UT-BSF/PLA, and BP-

T-BSF/PLA composites were studied by FTIR, DSC,

TGA, and SEM analysis. The addition of T-BSF in

PLA increased degree of crystallinity and delayed the

initial and final decomposition temperature for BP-T-

BSF/PLA composite compared to UT-BSF/PLA com-

posite and virgin PLA. This may be attributed to the

mercerization followed by BP treatment of BSF, which

facilitates effective adhesion between the T-BSF and

the PLA matrix. The SEM micrographs of the PLA,

UT-BF, T-BF, UT-SF, T-SF, and PLA-BSF composites

agree with the results obtained from FTIR, DSC, and

TGA analysis. Finally, we conclude that the chemical

modification is recommended to improve the perform-

ance of BSF as reinforcing fiber for PLA composites in

order to realize their applications in various fields of

engineering.

ACKNOWLEDGMENTS

The authors thank CIPET, at Chennai in Tamilnadu,

India for providing processing facilities to fabricate the bio-

composites of the present study, Harita NTI Ltd for provid-

ing material, Dr. Sujatha Priyadarshini, Department of

English, Anna University at Chennai for English proof cor-

rection, and Ms. Aparna from Anna University in assisting

the work.

NOMENCLATURE

NF Natural fibers

BF Banana fibers

SF Sisal fibers

BSF Banana/sisal fibers

UT-BF Untreated banana fiber

T-BF Treated banana fiber

UT-SF Untreated sisal fiber

T-SF Treated sisal fiber

PLA Poly(lactic acid)

BP Benzoyl peroxide

SEM Scanning electron microscope

Mw Molecular weight

GPa Giga Pascal

MPa Mega Pascal

UT-BSF/PLA Untreated banana and sisal fiber rein-

forced poly(lactic acid) composite

BP-T-BSF/PLA BP treated banana and sisal fiber rein-

forced poly(lactic acid) composite

Tg Glass transition temperature (8C)

Tc Crystallization temperature (8C)

Tm Melting temperature peak (8C)

Td Degradation temperature (8C)

To Oxidation temperature (8C)

DHm Enthalpy of melting (J/g)

DHc Enthalpy of crystallization (J/g)

DHom 93.7 enthalpy of fusion of 100% crys-

talline PLA (J/g-Joules/gram)

f Weight fraction of PLA

Xc Degree of crystallinity (%)

Td min Initial decomposition at minimum tem-

perature (8C)

Td max Final decomposition at maximum tem-

perature (8C)

Weight loss (%)

Residue weight (%)

KJ/m2 Kilo joules per meter square

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Banana/Sisal Fibers Reinforced Poly(lactic acid) Hybrid Biocomposites; Influence of Chemical Modification of BSF Towards Thermal Properties

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